The present invention relates to plasma source devices known as Wire-Ion-Plasma (WIP) electron guns.
WIP electron guns are known in the art and comprise high voltage discharge power sources used to drive gas-discharge lasers and to control high-pressure switching devices. An exemplary U.S. Patent disclosing a WIP E-gun is U.S. Pat. No. 4,025,818 entitled "Wire Ion Plasma Gun", issued to Giguere et al. and assigned to Hughes Aircraft Company. In addition, U.S. Pat. No. 3,970,892 entitled "Ion Plasma Electron Gun", issued to Wakalopulos and assigned to Hughes Aircraft discloses an ion plasma electron gun. Advantages of the WIP E-gun include the facts that no cathode heater power is required, instant start is provided, the controlling signal is obtained from a pulser at ground potential, and the WIP E-gun is not sensitive to poisoning by exposure to air or the switch gases. The WIP E-gun does require a source of low pressure gas, typically helium.
A disadvantage of known WIP E-guns has been the slow fall time (greater than fifteen microseconds) of the tail on the electron-beam current pulse. This has limited the usefulness of WIP E-guns in applications such as gas discharge laser pumping and electron beam controlled switching, which require a beam which turns "OFF" or interrupts in a time of less than a few microseconds. By way of example only, an electron-beam-controlled switch marketed by the assignee of the present invention employs a WIP E-gun which is the controlling element for the switch. This WIP E-gun has been characterized by a beam current fall time which increases with beam pulse length, reaching about fifteen microseconds following beam pulses of 10 to 100 microseconds in duration.
It is, therefore, an object of the present invention to provide an improvement in the pulse-shaping capability of WIP E-guns, especially for pulses of duration in excess of 10 microseconds.
It is another object of the present invention to provide a WIP E-gun having a reduced beam current fall time.
A further object of the invention is to identify the cause of the tail on the current pulse from a WIP E-gun, and provide a means for eliminating this tail.
Yet another object of the present invention is to provide a WIP E-gun employing an auxiliary grid adapted to significantly reduce the fall time of the current pulse.